Your "grid" elements are all floated, with margin-left: X%, and margin-right: -100%.

At first, i didn’t really know what to make of it.. now it’s a critical part of my toolbox.

What this lets you do is stack elements on top of each other, positioning purely by the margin-left attribute. The negative margin right allows you to use what almost looks like absolute positioning, but while still keeping the elements "in the flow" vertically.

That’s right.. with this trick, you can still have vertical flow while giving up horizontal flow.

Every time you’ve used absolute positioning to achieve a cross fade, but had to hard code the height value, you could have just used this instead.